CALGARY, Alberta (AP) -- A fossilized jaw found in an Alberta gravel pit may have cleared up a mystery for researchers wondering how brown bears originally made it across North America.

They probably migrated from what's now Alaska and the Yukon before glaciers covered the region, thousands of years before previously believed.

The findings are discussed in Friday's issue of the journal Science.

"It's like finding the missing link," said Paul Matheus, lead author of the paper and a paleobiologist at the University of Alaska.

Matheus said the discovery could have interest to archeologists trying to determine when humans first arrived in North America. The first appearance of large mammals in the region has been viewed as an indicator of when humans likely migrated south along the same route.

"One of the good litmus tests for habitability of that corridor and route down south has been, when do you actually see large mammal fossils show up, indicating there was a presence of game for people to eat?" Matheus said.

Matheus recognized the jaw bone as a brown bear's during a 2001 visit to the Provincial Museum of Alberta in Edmonton. Radiocarbon dating and DNA testing determined the fossil was about 26,000 years old and closely related to bears that today live in southern Canada and the northern United States.

Scientists previously believed brown bears first made it to central Alberta about 13,000 years ago when an ice-free corridor opened up and large mammals began to move south.

"The mystery has been more or less solved -- they walked through Alberta," said paleontologist Jim Burns, curator of ice-age fossils at the museum.

"This is the first evidence that shows they made the journey prior to the maximum glaciation when the passage was blocked," said Burns, co-author of the paper.

Brown bears migrated from Asia to North America through Siberia some 50,000 to 100,000 years ago across a stretch of the Bering Strait that was exposed during times of low sea level.

About 22,000 years ago, ice sheets sliding out of the Rocky Mountains and the lowlands west of Hudson's Bay came together to render the area impassable for about 9,000 years.

The upper and lower halves of the brown bear jaw were found in a gravel pit near Edmonton in 1998.